Light emitting device and method of manufacturing the same

ABSTRACT

A light emitting device is provided which has a structure for preventing degradation of a light emitting element due to water and oxygen contained in an interlayer insulating film formed between a TFT and the light emitting element. A TFT is formed on a substrate, an inorganic insulating film is formed on the TFT from an inorganic material and serves as a first insulating film, an organic insulating film is formed on the first insulating film from an organic material and serves as a second insulating film, and an inorganic insulating film is formed on the second insulating film from an inorganic material and serves as a third insulating film. Thus obtained is a structure for preventing the second insulating film from releasing moisture and oxygen. In order to avoid defect in forming the film, a portion of the third insulating film where a contact hole is formed is removed alone. Then, a light emitting element composed of an anode, an organic compound layer, and a cathode is formed on the third insulating film. A TFT and a light emitting element in a light emitting device of this application are connected to each other through a wire formed in a contact hole.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device using a lightemitting element from which florescence or phosphorescence is obtainedby applying an electric field to an element having a film containingorganic compound (hereinafter referred to as organic compound layer)between a pair of electrodes, and to a method of manufacturing the same.Note that the term light emitting device in this specification refers toan image display device, a light emitting device or a light source. Alsoincluded in the definition of the light emitting device are: a module inwhich a connector, such as an FPC (flexible printed circuit), a TAB(tape automated bonding) tape, or a TCP (tape carrier package), isattached to an organic light emitting device; a module in which aprinted wiring board is provided on the tip of a TAB tape or a TCP; anda module in which an IC (integrated circuit) is mounted directly to anorganic light emitting device by the COG (chip on glass) method.

2. Description of the Related Art

In recent years, a technique for forming a TFT on a substrate hasprogressed substantially, and application and development of activematrix type display devices is advancing. Especially, since a TFT usinga polysilicon film has a field-effect mobility (also called mobility)higher than that of a TFT using a conventional amorphous silicon film, ahigh speed operation is possible.

Such active matrix display devices are attracting attention because,various merits such as reduction of manufacturing cost, miniaturizationof a display device, improvement of a yield, and reduction of athroughput can be obtained by forming various circuits and elements onthe same substrate.

Among them, in a light emitting device in which light emitting elementsmade from an anode, an organic compound and a cathode are arranged in amatrix form (hereinafter referred to as active matrix light emittingdevice), a switching element formed of a TFT (hereinafter referred to asswitching TFT) is provided for each pixel, and a driving element forcontrolling current (hereinafter referred to as current control TFT) isoperated by the switching TFT, thereby making the light emittingelements emit light.

Note that a light emitting element is an element that emits light whenan electric field is applied. Light emission mechanism thereof is saidto be as follows. A voltage is applied to an organic compound filmsandwiched between electrodes to cause recombination of electronsinjected from the cathode and holes injected from the anode in theorganic compound film, and when the resultingly excited molecule(hereinafter referred to as molecular exciton) returns to base state, itreleases energy in the form of light emission.

In such a light emitting element, its organic compound layer is usuallyformed of a thin film having a thickness of less than 1 μm. In addition,the light emitting element does not need a backlight used inconventional liquid crystal displays because it is a self-luminouselement so that the organic compound layer itself emits light. The lightemitting element is therefore useful in manufacturing very thin andlight-weight devices, which is a great advantage.

With those features, including thinness, light-weightedness, quickresponse, and direct current low voltage driving, light emittingelements are attracting attention as the next-generation of flat paneldisplay elements. In addition, since the light emitting elements areself-luminous and have a wide viewing angle, relatively satisfactoryvisibility is provided and they are considered as effective especiallywhen used for display screens of electric appliance. However, thefollowing points were problems.

Usually, at least one or two TFTs are given for each pixel on thesubstrate. Further, through selection of TFT, a source signal line and agate signal line are formed in order to turn the device ON. Further, inorder to insulate the TFT from light emitting elements, an interlayerinsulating film which consists of insulated materials, such as siliconoxide and silicon nitride is formed on the TFT. Then, as the TFTthickness is 0.2 to 1 μm and uneven, this had to be avoided while pixelelectrodes were formed. Note that in this case, since the region inwhich the pixel electrodes are formed is substantially made smaller,there was a problem on that the aperture ratio of a pixel portion fell.

On the contrary, JP-10-189252A discloses the following technique. Thereare used a polyamide coating layer formed by spin coating and a layerformed by an etch-back method after silica is subjected to polymercoating, thereby forming an interlayer insulating film on the TFT toperform leveling. Further, the light emitting element is formed thereon,thereby improving the aperture ratio of the light emitting device.

In such light emitting devices, electric connection with a TFT formed ona substrate is made through an interlayer insulating film. Theinterlayer insulating film is formed from an inorganic materialcontaining silicon, such as silicon oxide, silicon nitride, and siliconoxynitride, or from an organic material such as polyimide, polyamide,acrylic, and other organic resins.

Inorganic materials have a characteristic that does not allow moistureand oxygen to transmit but have a defect of being cracked when they areformed into thick films.

In contrast, organic materials can be formed into thick films and thesurfaces of the films are fairly level. Accordingly, a film formed froman organic material is suitable as a film to level the surface above aTFT. However, organic materials also have disadvantages such as beingtransmissive of oxygen and transmissive or absorptive of moisture.

An organic compound layer constituting a light emitting element is veryweak against oxygen and moisture and is easily degraded. Oxygen andmoisture cause degradation of a light emitting element and accordinglycause dark spot or other degradation of a light emitting device.

When a second interlayer insulating film formed of an organic materialand a third interlayer insulating film formed of an inorganic materialare layered, there is a technical difficulty in patterning the laminate.Specifically, the third interlayer insulating film peels off (peeling)at an edge of a contact hole where a first interlayer insulating filmand the second interlayer insulating film overlap and are exposed insection. The contact hole is formed in the laminate in order to form awire for connecting the TFT with an electrode of the light emittingelement.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above, and objects ofthe present invention are therefore to provide a structure forpreventing degradation of a light emitting element due to moisture andoxygen contained in an interlayer insulating film that is formed betweena TFT and the light emitting element and to solve the problem thatarises when an insulating film formed of an inorganic material and aninsulating film formed of an organic material are layered.

The present invention is characterized in that a TFT is formed on asubstrate, an inorganic insulating film is formed on the TFT from aninorganic material and serves as a first insulating film, an organicinsulating film is formed on the first insulating film from an organicmaterial and serves as a second insulating film, an inorganic insulatingfilm is formed on the second insulating film from an inorganic materialand serves as a third insulating film, and a light emitting elementcomposed of an anode, an organic compound layer, and a cathode is formedon the third insulating film.

The present invention is characterized by being structured such that asecond insulating film and a third insulating film are layered toprevent the second insulating film from releasing its moisture andoxygen and that no third insulating film is formed in a portion where acontact hole is formed.

Specifically, the above structure is obtained as follows: a firstinsulating film, a second insulating film, and a third insulating filmare layered, a conductive film for a first electrode of a light emittingelement is formed, the conductive film is patterned to form the firstelectrode while at the same time the third insulating film is partiallyetched, and a contact hole is formed in the second insulating film whosesurface has been exposed by etching, in the first insulating film, andin a gate insulating film.

A structure of the present invention disclosed herein is a lightemitting device having: a TFT formed on an insulating surface; a firstinsulating film formed on the TFT from an inorganic material; a secondinsulating film formed on the first insulating film from an organicmaterial; and a light emitting element composed of a first electrode, anorganic compound layer, and a second electrode, the device characterizedin that a third insulating film is formed from an inorganic material andis positioned so as to overlap the first electrode.

Also, according to another structure of the present invention, there isprovided a light emitting device including: a TFT formed on aninsulating surface; a first insulating film formed on the TFT from aninorganic material; a second insulating film formed on the firstinsulating film from an organic material; a contact hole formed in thefirst insulating film and the second insulating film; a light emittingelement composed of a first electrode, an organic compound layer, and asecond electrode; and a third insulating film formed from an inorganicmaterial between the second insulating film and the first electrodewhile overlapping the first electrode, in which the TFT is electricallyconnected to the first electrode through a wire that is formed in thecontact hole.

Also, according to another structure of the present invention, there isprovided a light emitting device including: a TFT formed on aninsulating surface; a first insulating film formed on the TFT from aninorganic material; a second insulating film formed on the firstinsulating film from an organic material; a contact hole formed in agate insulating film of the TFT, the first insulating film, and thesecond insulating film; a light emitting element composed of a firstelectrode, an organic compound layer, and a second electrode; and athird insulating film formed from an inorganic material between thesecond insulating film and the first electrode while overlapping thefirst electrode, in which a wire is formed in the contact hole and comesinto contact with the first insulating film, the second insulating film,and the gate insulating film, and in which the wire electricallyconnects the TFT with the first electrode.

In the above structures, employable inorganic materials are a siliconoxynitride film and a silicon nitride film and, desirably, the siliconcontent ratio thereof is 25.0 atomic % or higher and 35.0 atomic % orlower and the nitrogen content ratio thereof is 35.0 atomic % or higherand 65.0 atomic % or lower. A silicon oxide film may also be used but asilicon oxynitride film or a silicon nitride film is preferred takinginto consideration the ability of blocking an alkaline metal and thelike.

In the above structures, employable organic materials arethermally-curable or photo-curable organic resin materials, such asacrylic, polyimide, polyamide, polyimideamide, and BCB(benzocyclobutene).

Also, according to another structure of the present invention, there isprovided a method of manufacturing a light emitting device, including:forming a TFT on an insulating surface; forming a first insulating filmon the TFT from an inorganic material; forming a second insulating filmon the first insulating film by application from an organic material;forming a third insulating film on the second insulating film bysputtering from an inorganic material; forming a conducting film on thethird insulating film, the conductive film serving as a first electrodeof a light emitting element; forming the first electrode from theconductive film by first etching using a mask; and removing the thirdinsulating film by second etching except an area that overlaps the firstelectrode.

Further, according to another structure of the present invention, thereis provided a method of manufacturing a light emitting device,including: forming a TFT on an insulating surface; forming a firstinsulating film on the TFT from an inorganic material; forming a secondinsulating film on the first insulating film by application from anorganic material; forming a third insulating film on the secondinsulating film by sputtering from an inorganic material; forming aconducting film on the third insulating film, the conductive filmserving as a first electrode of a light emitting element; forming thefirst electrode from the conductive film by first etching using a mask;removing the third insulating film by second etching except an area thatoverlaps the first electrode; forming a contact hole in the firstinsulating film, the second insulating film, and a gate insulating filmof the TFT; forming a wire in the contact hole; bringing the wire intocontact with the TFT and the first electrode; forming an organiccompound layer on the first electrode; and forming a second electrode ofthe light emitting element on the organic compound layer.

In the above structures, an inorganic material is formed into a film byvapor-phase film formation methods such as sputtering, reactivesputtering, ion beam sputtering, ECR (electron cyclotron resonance)sputtering, and ion evaporation. These film formation methods are tomake an atom or molecule adhere onto a substrate physically. Thereforethe atom or molecule hardly reacts with the interlayer insulating filmpreviously formed from an organic material, and the methods have no fearof transforming the atom or molecule chemically. In addition, themethods are characterized in that a dense film can be formed even whenthe temperature ranges between room temperature and 300° C. The film hasa characteristic of preventing transmission of oxygen and moisture.

If one of the sputtering methods given in the above is used, aninorganic insulating film which has satisfactory light transmittance andwhich mainly contains silicon or nitrogen can be formed at a substratetemperature ranging from room temperature to 300° C. The inorganicinsulating film is interposed between an interlayer insulating filmformed of an organic material and a light emitting element that iscomposed of an anode, a cathode, and an organic compound layer. Thisprevents the interlayer insulating film formed of an organic materialfrom releasing oxygen and moisture and therefore degradation of thelight emitting element can be avoided.

When the inorganic insulating film mainly containing silicon andnitrogen is formed by sputtering, a target mainly containing silicon isused and argon, nitrogen, oxygen, or nitrogen oxide is employed assputtering gas. The composition ratio of nitrogen and oxygen in theinorganic insulating film mainly containing silicon and nitrogen variesdepending on the gas flow rate during film formation. In thisspecification, a film having nitrogen as the main ingredient other thansilicon in the composition ratio is called a silicon nitride filmwhereas a film having oxygen and nitrogen as the main ingredients otherthan silicon in the composition ratio is called a silicon oxynitridefilm.

If the inorganic insulating film mainly containing silicon and nitrogenis formed by one of the above sputtering methods using silicon as thetarget and gas that contains noble gas and nitrogen, the film obtainedcan have a silicon content ratio of 25.0 atomic % or higher and 35.0atomic % or lower and a nitrogen content ratio of 35.0 atomic % orhigher and 65.0 atomic % or lower.

The above process does not include heating a substrate at 300° C. orhigher. Therefore, the process is also applicable to cases where a TFTis formed on a resin substrate or a flexible (plastic) substrate.

In the above structures, an inorganic insulating film is formed from aninorganic material, a transparent conductive film is formed on theinorganic insulating film, a mask is formed by photolithography, and thetransparent conductive film is subjected to first etching to form afirst electrode. The first etching is followed by second etching withoutremoving the mask, thereby etching a portion of the inorganic insulatingfilm that does not overlap the mask. There are two types of etchingmethods: wet etching and dry etching. In the present invention, thefirst etching uses wet etching and the second etching uses dry etching.

Light emission obtained from a light emitting device of the presentinvention is light emission from singlet excitation or light emissionfrom triplet excitation, or both.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram illustrating an element structure in a lightemitting device of the present invention;

FIGS. 2A to 2D are diagrams illustrating an element structure in a lightemitting device of the present invention;

FIGS. 3A to 3C are diagrams illustrating an element structure in a lightemitting device of the present invention;

FIGS. 4A to 4C are diagrams illustrating an element structure in a lightemitting device of the present invention;

FIGS. 5A to 5C are diagrams illustrating a process of manufacturing alight emitting device of the present invention;

FIGS. 6A to 6C are diagrams illustrating a process of manufacturing alight emitting device of the present invention;

FIGS. 7A to 7D are diagrams illustrating an element structure in a lightemitting device of the present invention;

FIGS. 8A and 8B are diagrams illustrating a pixel portion structure thatcan be used in the present invention;

FIGS. 9A and 9B are diagrams illustrating the exterior of a lightemitting device of the present invention; and

FIGS. 10A to 10H are diagrams showing examples of an electronicappliance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

An embodiment of the present invention is described with reference toFIG. 1. FIG. 1 shows the sectional structure of a light emitting elementformed in a pixel portion of a light emitting device in the presentinvention. In the description here, the light emitting element is ofdownward emission type and light generated in its organic compound layeris taken out from the substrate side (from the side of a first electrodedescribed later).

In FIG. 1, thin film transistors (TFTs) are formed on a substrate 101.The TFTs shown here are a current controlling TFT 202 and a switchingTFT 201. The current controlling TFT 202 is electrically connected to afirst electrode 111 of a light emitting element 118 and has a functionof controlling the current supplied to the light emitting element 118.The switching TFT 201 is for controlling a video signal applied to agate electrode 106 of the current controlling TFT 202. In thisembodiment, the current controlling TFT 202 is a p-channel TFT and theswitching TFT 201 is an n-channel TFT.

The substrate 101 has to be transmissive of light and thereby a glasssubstrate is used. A quartz substrate, a resin substrate, or a flexible(plastic) substrate material may be used instead. The TFTs each have anactive layer, which has at least a channel formation region 102, asource region 103, and a drain region 104.

The active layer of each TFT is covered with a gate insulating film 105.A gate electrode 106 overlaps the channel formation region 102 with thegate insulating film 105 sandwiched therebetween. The gate electrode 106is covered with a first interlayer insulating film 108. A secondinterlayer insulating film 109 is formed on the first interlayerinsulating film 108. A third interlayer insulating film 110 is formed onthe second interlayer insulating film 109.

The first interlayer insulating film 108 is formed from an inorganicmaterial containing silicon, such as silicon oxide, silicon nitride,silicon oxynitride, or an applied silicon oxide film (SOG: Spin OnGlass). The second interlayer insulating film 109 is formed from anorganic material such as polyimide, polyamide, acrylic (includingphotosensitive acrylic), or BCB (benzocyclobutene). The third interlayerinsulating film 110 is formed from an inorganic material containingsilicon, such as silicon oxide, silicon nitride, silicon oxynitride, orSOG.

After the third interlayer insulating film 110 is formed, a transparentconductive film is formed and patterned to form the first electrode 111that is an electrode through which light is taken out.

In this embodiment, the first electrode 111 functions as an anode.Therefore the transparent conductive film used here is formed from amaterial having a large work function, 4.5 eV or more. Specifically, alight-transmissive conductive film such as an indium oxide-tin (ITO:indium tin oxide) film or an indium zinc oxide (IZO) film obtained bymixing 2 to 20% of zinc oxide (ZnO) with indium oxide can be employed.Long period elements belonging to Groups 3 to 11 in the periodic table,such as gold (Au), platinum (Pt), Nickel (Ni), tungsten (W), andtitanium (Ti), can also be employed as conductive materials.

On the other hand, if a second electrode formed later serves as anelectrode through which light is taken out, the first electrode 111 isformed from a light-transmissive anode material. In this case, longperiod elements belonging to Groups 3 to 11 in the periodic table, suchas gold (Au), platinum (Pt), Nickel (Ni), tungsten (W), and titanium(Ti), are formed into a film whose thickness is set to obtain 10% orless transmittance for visible light.

The third interlayer insulating film 110 and the transparent conductivefilm 120 are now finished and the device at this point is shown in FIG.2A. Components in FIG. 2A that are identical with those in FIG. 1 aredenoted by the same symbols.

On the transparent conductive film 120, a mask 121 is formed byphotolithography to etch the transparent conductive film 120. Wetetching is used for etching of the transparent conductive film 120. As aresult, the first electrode 111 is formed by patterning (FIG. 2B).

Without removing the mask 121, the third interlayer insulating film 110is etched by dry etching. In this etching, a portion of the thirdinterlayer insulating film 110 that is covered with the mask 121 andthat overlaps the first electrode 111 is not etched and left whereas therest of the third interlayer insulating, film 110 is etched away (FIG.2C).

The mask 121 is removed and then contact holes reaching the source ordrain of the TFTs are formed in the second interlayer insulating film109, the first interlayer insulating film 108, and the gate insulatingfilm 105. After the contact holes are formed, wires 112 to 115 areformed and electrically connected to the source regions or drain regionsof the TFTs (FIG. 2D).

The third interlayer insulating film 110 structured as shown in FIG. 1is formed between the second interlayer insulating film 109 and thefirst electrode 111 through these steps. In this way, the thirdinterlayer insulating film 110 formed of an inorganic material preventsthe second interlayer insulating film 109 formed of an organic materialfrom releasing moisture and oxygen to the light emitting element 118side. In addition, the contact holes reaching the source regions ordrain regions of the TFTs are formed in portions of the first interlayerinsulating film and second interlayer insulating film from which thethird interlayer insulating film has been removed. Accordingly, theproblem of peeling, which is caused by forming a contact hole in alaminate portion of a second interlayer insulating film and a thirdinterlayer insulating film, can be avoided.

The first electrode 111 is connected to a drain region 104 of thecurrent controlling TFT 202 through the wire 114. The luminance of lightemitted from the light emitting element 118 is controlled by the levelof current supplied from the current controlling TFT 202 to the firstelectrode 111.

As shown in FIG. 1, the ends of the first electrode 111 and the wires(112 to 115) are covered with an insulating layer 116. The insulatinglayer 116 is formed from an inorganic material containing silicon, suchas silicon oxide, silicon nitride, silicon oxynitride, or an appliedsilicon oxide film (SOG: Spin On Glass), or an organic material such aspolyimide, polyamide, acrylic (including photosensitive acrylic), or BCB(benzocyclobutene). The thickness of the insulating layer 116 is set to0.1 to 2 μm. In particular, when formed from a material containingsilicon, such as silicon oxide, silicon nitride, or silicon oxynitride,the insulating layer 116 desirably has a thickness of 0.1 to 0.3 μm.

An opening positioned so as to overlap the first electrode 111 is formedin the insulating layer 116, thereby obtaining an insulating layer 119.

An organic compound layer 120 is formed on the first electrode (anode)111. The first electrode 111, the organic compound layer 120, and asecond electrode (cathode) 117 that is formed on the organic compoundlayer 120 constitute the light emitting element 118. The material of theorganic compound layer 120 may be a low-molecular weight material or ahigh-molecular weight material. The second electrode (cathode) 117 isformed from a material having a small work function (specifically, 3.8eV or less). An element belonging to Group 1 or 2 of the periodic table,namely, an alkaline metal, an alkaline earth metal, an alloy or compoundcontaining those metals, or a transitional metal including a rare-earthmetal can be employed for the second electrode 117. The second electrode(cathode) 117 is formed by evaporation or sputtering.

In Embodiment 1, the first electrode 111 is formed from a transparentconductive film to serve as an anode and therefore light generated byrecombination of carriers in the organic compound layer 120 is emittedfrom the first electrode 111 side. The second electrode 117 is desirablyformed of a light-shielding material.

In this embodiment, a buffer layer (not shown in the drawing) isprovided in the interface between the organic compound layer 120 and thesecond electrode 117. The material of the buffer layer can be bariumfluoride (BaF₂), calcium fluoride (CaF₂), cesium fluoride (CsF), or thelike. The thickness of the buffer layer has to be about 1 nm. Othermaterials that can be used for the buffer layer include cesium (Cs),barium (Ba), calcium (Ca), a magnesium alloy (Mg:Ag), and lanthanoids.The buffer layer here is formed from barium fluoride (BaF₂) to athickness of 1 nm. On the buffer layer, an Al film is formed to athickness of 100 nm as the second electrode 117. In this embodiment, thebuffer layer is included in the second electrode 117.

Through the above process, a light emitting device having the firstelectrode 111, the organic compound layer 120, and the second electrode117 is obtained.

Embodiment 2

Embodiment 2 describes in detail a method of manufacturing a pixelportion and TFTs (an n-channel TFT and a p-channel TFT) of a drivingcircuit provided in the periphery of the pixel portion on the samesubstrate at the same time. The description is given with reference toFIGS. 3A to 6C.

First, a base insulating film 601 is formed on a substrate 600. After afirst semiconductor film having a crystal structure is obtained, thefilm is etched into desired shapes to form semiconductor layers 602 to605 that are separated from one another like islands.

The substrate 600 is a glass substrate, a quartz substrate, or a ceramicsubstrate. For the base insulating film 601, a silicon oxynitride film601 a with a thickness of 50 nm (preferably 10 to 200 nm) is formed byplasma CVD at 400° C. using SiH₄, NH₃, and N₂O as material gas. Next, asilicon oxynitride film 601 b with a thickness of 100 nm (preferably 50to 200 nm) is formed by plasma CVD at 400° C. using SiH₄ and N₂O asmaterial gas and laid on 601 a. Then a semiconductor film having anamorphous structure (here an amorphous silicon film) is formed by plasmaCVD at 300° C. using SiH₄ as material gas to a thickness of 54 nm(preferably 25 to 80 nm).

The base film 601 in this embodiment has a two-layer structure but itmay be a single layer or two or more layers of the above insulatingfilms. The material of the semiconductor film is not limited butsilicon, a silicon germanium (Si_(X)Ge_(1-X) (X=0.0001 to 0.02)) alloy,or the like is preferred and these may be formed into a film by a knownmethod (sputtering, LPCVD, plasma CVD, or the like).

Next, the semiconductor film having an amorphous structure iscrystallized to obtain a semiconductor film having a crystal structure.Crystallization here can employ a known crystallization technique suchas a solid-phase growth method or laser crystallization.

If laser crystallization is employed, a pulse oscillation type orcontinuous wave excimer laser, YAG laser, YVO₄ laser, or YLF laser canbe used. The second to fourth harmonic of a YAG laser, YVO₄ laser, orYLF laser is utilized. In this case, laser light emitted from the laseroscillator is collected by an optical system into a linear beam beforeit irradiates the semiconductor film. Crystallization conditions can beset to suit individual cases.

In another crystallization method, the semiconductor film beforecrystallization is doped with nickel or other metal elements having acatalytic function over crystallization of a semiconductor. Forinstance, a solution containing nickel is held to the top face of theamorphous silicon film, the amorphous silicon film is subjected todehydrogenation (at 500° C. for an hour) and then thermalcrystallization (at 550° C. for four hours), and the film is thenirradiated with the second harmonic of a continuous wave laser selectedfrom a YAG laser, a YVO₄ laser, and a YLF laser to improve itscrystallinity.

Next, a resist mask is formed on the surface of the obtained siliconfilm with a crystal structure (also called a polysilicon film). Thesilicon film is etched into desired shapes to form the semiconductorlayers 602 to 605 that are separated from one another like islands.After the semiconductor layers are formed, the resist mask is removed.

The obtained semiconductor layers may be doped with an impurity elementthat give the p type or n type conductivity in order to control thethreshold (Vth) of the TFTs. Impurity elements known to give the p typeconductivity to a semiconductor are Group 13 elements in the periodictable, such as boron (B), aluminum (Al), and gallium (Ga). Impurityelements known to give the n type conductivity to a semiconductor areGroup 15 elements in the periodic table, typically, phosphorus (P) orarsenic (As).

Next, a gate insulating film 607 is formed to cover the semiconductorlayers 602 to 605. The gate insulating film 607 is an insulating filmcontaining silicon and is formed by plasma CVD or sputtering from aninorganic insulating material such as silicon oxide or siliconoxynitride to a thickness of 40 to 150 nm. The gate insulating film maybe a single layer or laminate of insulating films containing silicon.

Next, as shown in FIG. 3A, a first conductive film 608 with a thicknessof 20 to 100 nm and a second conductive film 609 with a thickness of 100to 400 nm are layered on the gate insulating film 607. In thisembodiment, a tantalum nitride film with a thickness of 30 nm and atungsten film with a thickness of 370 nm are layered sequentially on thegate insulating film 607.

The conductive material of the first conductive film and secondconductive film can be an element selected from the group consisting ofTa, W, Ti, Mo, Al, and Cu, or an alloy or compound mainly containing theabove-mentioned elements. Alternatively, the first conductive film andthe second conductive film may be semiconductor films, typicallypolycrystalline silicon films, doped with phosphorus or otherimpurities, or may be Ag—Pd—Cu alloy films.

Next, resist masks 610 to 613 are formed by a light exposure process asshown in FIG. 3B. Then first etching treatment is conducted for forminggate electrodes and wires. The first etching treatment employs first andsecond etching conditions. ICP (inductively coupled plasma) etching ispreferred for the etching. The films can be etched to have desired tapershapes by using ICP etching and suitably adjusting the etchingconditions (the amount of power applied to a coiled electrode, theamount of power applied to an electrode on the substrate side, thetemperature of the electrode on the substrate side, etc.). For etchinggas, a suitable one can be chosen from chlorine-based gas, typically,Cl₂, BCl₃, SiCl₄, or CCl₄, fluorine-based gas, typically, CF₄, SF₆, orNF₃, and O₂.

In this embodiment, the substrate side (sample stage) also receives anRF (13.56 MHz) power of 150 W to apply a substantially negativeself-bias voltage. The area of the substrate-side electrode is 12.5cm×12.5 cm. The coiled electrode (here, a quartz disc provided with acoil) is a disc having a diameter of 25 cm.

The first etching conditions in this embodiment include employing ICP(inductively coupled plasma) etching, using CF₄, Cl₂, and O₂ as etchinggas, setting the gas flow rate ratio thereof to 25:25:10 (sccm), andapplying an RF (13.56 MHz) power of 500 W to a coiled electrode at apressure of 1 Pa to generate plasma for etching. The substrate side(sample stage) also receives an RF (13.56 MHz) power of 150 W to apply asubstantially negative self-bias voltage. The W film is etched underthese first etching conditions to taper the first conductive layeraround the edges.

Thereafter the first etching conditions are switched to the secondetching conditions without removing the resist masks 610 to 613. Thesecond etching conditions include using CF₄ and Cl₂ as etching gas,setting the gas flow rate ratio thereof to 30:30 (sccm), and giving anRF (13.56 MHz) power of 500 W to a coiled electrode at a pressure of 1Pa to generate plasma for etching for about 30 seconds. The substrateside (sample stage) also receives an RF power (13.56 MHz) of 20 W toapply a substantially negative self-bias voltage. Under the secondetching conditions where a mixture of CF₄ and Cl₂ is used, the W filmand the TaN film are etched to the same degree.

Through the first etching treatment, first shape conductive layers 615to 618 consisting of the first conductive layer and the secondconductive layer (first conductive layers 615 a to 618 a and secondconductive layers 615 b to 618 b) are formed. The insulating film 607serving as the gate insulating film is etched by 10 to 20 nm. Thusobtained is a gate insulating film 620 in which regions that are notcovered with the first shape conductive layers 615 to 618 are thinned.

Next follows the second etching treatment with the resist masks kept inplace. Here, SF₆, Cl₂ and O₂ are used as etching gas to etch the W filmselectively. The gas flow rate ratio thereof is set to 24:12:24 (sccm),and an RF (13.56 MHz) power of 700 W is given to a coiled electrode at apressure of 1.3 Pa to generate plasma for etching. The substrate side(sample stage) also receives an RF power (13.56 MHz) of 10 W to apply asubstantially negative self-bias voltage.

Second conductive layers 621 b to 624 b are formed through the secondetching treatment. On the other hand, the first conductive layers arehardly etched in this treatment and become first conductive layers 621 ato 624 a. The first conductive layers 621 a to 624 a and the firstconductive layers 615 a to 618 a have almost the same size.

The resist masks are removed and then the first doping treatment isconducted to obtain the state of FIG. 4A. The doping treatment employsion doping or ion implantation. The ion doping conditions includesetting the dose to 6.0×10¹³ atoms/cm² and the acceleration voltage to60 to 100 keV. As an impurity element that gives the n typeconductivity, typically, phosphorus (P) or arsenic (As) is used. In thiscase, the first and second conductive layers 621 to 624 serve as masksagainst the impurity element that gives the n type conductivity andfirst impurity regions 626 to 629 are formed in a self-aligning manner.The first impurity regions 626 to 629 are doped with the impurityelement that gives the n type conductivity in a concentration of 1×10¹⁶to 1×10¹⁷/cm³. Here, a region having the same concentration range as thefirst impurity regions is called an n⁻ region.

Next, as shown in FIG. 4B, resist masks 631 to 633 are formed for thesecond doping treatment. The mask 631 is to protect a channel formationregion and surrounding regions of a semiconductor layer for forming thep-channel TFT of the driving circuit. The mask 632 is to protect achannel formation region and surrounding regions of a semiconductorlayer for forming a TFT of the pixel portion.

The ion doping conditions in the second doping treatment include settingthe dose to 3.0×10¹⁵ atoms/cm² and the acceleration voltage to 60 to 100keV. In the second doping treatment, impurity regions are formed in thesemiconductor layers in a self-aligning manner with the secondconductive layer 621 b as a mask. It is certain that the regions coveredwith the masks 631 to 633 are not doped with the impurity element. Inthis way, second impurity regions 634 and 635 and a third impurityregion 637 are formed. The second impurity regions 634 and 635 are dopedwith the impurity element that gives the n type conductivity in aconcentration of 1×10²⁰ to 1×10²¹/cm³. Here, a region having the sameconcentration range as the second impurity regions is called an n⁺region.

The impurity concentration in the third impurity region is lower than inthe second impurity regions because of the first conductive layers. Thethird impurity region is doped with the impurity element that gives then type conductivity in a concentration of 1×10¹⁸ to 1×10¹⁹/cm³. Sincethe third impurity region is doped through the tapered portions of thefirst conductive layers, it has a concentration gradient that increasesthe impurity concentration toward the edges of the tapered portions.Here, a region having the same concentration range as the third impurityregion is called an n⁻ region. The region that is covered with the mask632 is not doped with the impurity element and becomes a first impurityregion 638.

The resist masks 631 to 633 are removed and new resist masks 639 and 640are formed as shown in FIG. 4C for the third doping treatment.

Through the third doping treatment, fourth impurity regions 641 and 642and fifth impurity regions 643 and 644 doped with an impurity elementthat gives the p type conductivity are formed in the semiconductor layerfor forming the p-channel TFT and the semiconductor layer for formingcapacitor storage in the driving circuit.

The fourth impurity regions 641 and 642 are doped with an impurityelement that gives the p type conductivity in a concentration of 1×10²⁰to 1×10²¹/cm³. The fourth impurity regions 641 and 642 are the regionsthat are doped with phosphorus (P) in the previous step (n⁻ region). Nowthat the fourth impurity regions are doped with an impurity element thatgives the p type conductivity in a concentration 1.5 to 3 times theconcentration of phosphorus, the conductivity type of the fourthimpurity regions is p type. Here, a region having the same concentrationrange as the fourth impurity regions is called a p⁺ region.

The fifth impurity regions 643 and 644 are formed in the regions thatoverlaps the tapered portions of the second conductive layers 125 a, andare doped with an impurity element that gives the p type conductivity ina concentration of 1×10¹⁸ to 1×10²⁰/cm³. Here, a region having the sameconcentration range as the fifth impurity regions is called a p⁻ region.

Through the above steps, the impurity regions having the n type or ptype conductivity are formed in the respective semiconductor layers. Theconductive layers 621 to 624 serve as gate electrodes of the TFTs.

Next, an insulating film is formed to cover almost the entire surface.In this embodiment, the insulating film is formed from an inorganicmaterial and is called a first interlayer insulating film 645.Specifically, a silicon nitride film is formed by plasma CVD to athickness of 100 nm. It is certain that the insulating film is notlimited to the silicon nitride film but may be a single layer orlaminate of other insulating films containing silicon.

Next, the step of activating the impurity elements used in doping of thesemiconductor layers is performed. The activation step is achieved byrapid thermal annealing (RTA) using a lamp light source, or YAG laser orexcimer laser irradiation from the back side, or heat treatment using afurnace, or a combination of these methods.

Then heat treatment (at 300 to 550° C. for 1 to 12 hours) is conductedto hydrogenate the semiconductor layers (FIG. 5A). This step is toterminate dangling bonds in the semiconductor layers using hydrogen thatis contained in the first interlayer insulating film 645. Thesemiconductor layers can be hydrogenated irrespective of presence orabsence of the gate insulating film 620 that is a silicon oxide film.

On the first interlayer insulating film 645, a second interlayerinsulating film 646 is formed from an organic insulating material. Inthis embodiment, an acrylic film is formed by application to a thicknessof 1.0 to 2.0 μm. Acrylic, polyimide, polyamide, polyimideamide, BCB(benzocyclobutene) or the like can be used as an organic insulatingmaterial.

By forming the second interlayer insulating film 646 from an organicmaterial, the surface can be leveled well. Organic materials aregenerally low in dielectric constant and therefore can reduce parasiticcapacitance. However, organic materials are hygroscopic and are notsuitable to form a protective film. Accordingly, it is preferable tocombine an organic insulating film serving as the second interlayerinsulating film with a silicon oxide film, silicon oxynitride film, orsilicon nitride film that is formed as the first interlayer insulatingfilm 645 as in this embodiment.

On the second interlayer insulating film 646, a third interlayerinsulating film 647 is formed from an inorganic material.

The third interlayer insulating film 647 is a silicon nitride film orsilicon oxynitride film formed by sputtering. In this embodiment, asilicon nitride film is formed to a thickness of 100 nm. Silicon isemployed as the target, and the sputtering gas are N₂ and Ar with thegas flow rate ratio thereof set to 20:20 (sccm). To form the film, thepressure is set to 0.4 Pa, the power is set to 800 W, and a circulartarget with a radius of 6 inches is used. The film formation temperatureranges between room temperature and 200° C. In this embodiment, the filmis formed at 200° C.

On the third interlayer insulating film 647, a transparent conductivefilm 648 transmissive of light is formed. The transparent conductivefilm 648 is an indium tin oxide (ITO) film, or transparent conductivefilm obtained by mixing 2 to 20% of zinc oxide (ZnO) with indium oxide,formed by sputtering to a thickness of 110 nm.

After a resist mask is formed on the transparent conductive film 648,the film is etched by wet etching using an acid-based etchant to form afirst electrode 649.

With the mask kept in place, the third interlayer insulating film 647 isetched by dry etching. Etching conditions for etching the thirdinterlayer insulating film 647 include using CF₄, O₂, and He as materialgas, setting the gas flow rate ratio thereof to 60:40:35 (sccm), givingan RF (13.56 MHz) power of 400 W to the substrate side (sample stage),and giving an RF (13.56 MHz) power of 450 W to a coiled electrode at apressure of 53.2 Pa to generate plasma.

Through the above steps, the third interlayer insulating film 647 isetched away except a portion that overlaps the first electrode 649. Thusobtained is the structure shown in FIG. 5C in which the regionoverlapping the first electrode 649 alone has the third interlayerinsulating film 647.

Contact holes reaching source regions or drain regions of the TFTs areformed next. The contact holes are formed by etching the secondinterlayer insulating film 646, the first interlayer insulating film645, and the gate insulating film 620 through dry etching under thefollowing conditions.

The second interlayer insulating film 646 is etched first. Etchingconditions for etching the second interlayer insulating film 646 includeusing CF₄, O₂, and He as material gas, setting the gas flow rate ratiothereof to 5:95:40 (sccm), giving an RF (13.56 MHz) power of 500 W tothe substrate side (sample stage), and giving an RF (13.56 MHz) power of450 W to a coiled electrode at a pressure of 66.5 Pa to generate plasma.

The first interlayer insulating film 645 is etched next. Etchingconditions for etching the first interlayer insulating film 645 includeusing CF₄, O₂, and He as material gas, setting the gas flow rate ratiothereof to 40:60:35 (sccm), giving an RF (13.56 MHz) power of 400 W tothe substrate side (sample stage), and giving an RF (13.56 MHz) power of450 W to a coiled electrode at a pressure of 40 Pa to generate plasma.

Then the gate insulating film 620 is etched. Etching conditions foretching the gate insulating film 620 include using CHF₃ as material gasand setting the gas flow rate ratio thereof to 35 (sccm).

Thereafter, wires are formed from Al, Ti, Mo, W, or the like. Desirably,the electrodes and pixel electrode are formed from materials havingexcellent reflectance, such as a film mainly containing Al, a filmmainly containing Ag, or a laminate of these films. Thus obtained arewires 651 to 658 (FIG. 6A).

Next, a first insulating layer 670 is formed from an organic material.The first insulating layer 670 here is a photosensitive acrylic film.Instead, polyimide, polyamide, acrylic, or BCB (benzocyclobutene) may beused for the first insulating layer.

Specifically, the first insulating layer 670 is obtained by forming aphotosensitive acrylic film through spin coating to a thickness of 1.45μm, patterning the film through photolithography, and etching the filmto form an opening so that the opening coincides with the firstelectrode (anode) 649 (FIG. 6B).

Etching conditions for forming the first insulating layer include usingCF₄, O₂, and He as material gas, setting the gas flow rate ratio thereofto 10:90:40 (sccm), and setting the pressure to 66.5 Pa.

Next, a second insulating layer 671 is formed from an inorganicmaterial. The second insulating layer 671 here is a silicon nitridefilm. Other materials containing silicon, such as silicon oxide, siliconoxynitride, or SOG, may be used instead.

To be specific, a silicon nitride film is formed by sputtering to athickness of 100 nm. To form the silicon nitride film, silicon isemployed as the target, N₂ and Ar are used as material gas, and the gasflow rate ratio thereof is set to 20:20 (sccm). The film formationpressure is set to 0.4 Pa, the power is set to 800 W, and a circulartarget with a radius of 6 inches is used. The film formation temperatureranges between room temperature and 200° C. In this embodiment, the filmis formed at 200° C. The obtained silicon nitride film is patterned byphotolithography and then etched to form an opening so that the openingcoincides with the first electrode (anode) 649. The second insulatinglayer 671 is thus formed (FIG. 6B).

Etching conditions for forming the second insulating layer 671 includeusing CF₄, O₂, and He as material gas, setting the gas flow rate ratiothereof to 60:40:35 (sccm), and setting the pressure to 53.2 Pa.

Next, an organic compound layer 672 is formed by evaporation on thefirst electrode (anode) 649 that is exposed in the opening of the secondinsulating layer 671 (FIG. 6B).

Although only one pixel is shown here, the pixel portion of thisembodiment has plural pixels and each pixel has one of three types oforganic compound layers: an organic compound layer that emits red light;an organic compound layer that emits green light; and an organiccompound layer that emits blue light, to display a full-color image.Combinations of organic compounds for forming these three types oforganic compound layers are described with reference to FIGS. 7A to 7D.

A light emitting element shown in FIG. 7A is composed of a firstelectrode (anode) 701, an organic compound layer 702, and a secondelectrode (cathode) 703. The organic compound layer 702 has a laminatestructure consisting of a hole transporting layer 704, a light emittinglayer 705, a blocking layer 706, and an electron transporting layer 707.The second electrode 703 has a cathode buffer layer 708 that is incontact with the organic compound layer 702 (here, the electrontransporting layer 707). FIG. 7B shows materials constituting a lightemitting element that emits red light and their thicknesses. FIG. 7Cshows materials constituting a light emitting element that emits greenlight and their thicknesses. FIG. 7D shows materials constituting alight emitting element that emits blue light and their thicknesses.

An organic compound layer that emits red light is formed first.Specifically, an organic compound capable of transporting holes isformed into a 40 nm thick film as the hole transporting layer 704 on thefirst electrode (anode) 701 previously formed. The hole transportingorganic compound here is4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereinafter referredto as α-NPD). Then 2, 3, 7, 8, 12, 13, 17, 18-octaethyl-21H,23H-porphyrin-platinum (hereinafter referred to as PtOEP), which is aluminous organic compound, and 4,4′-dicarbazole-biphenyl (hereinafterreferred to as CBP), which is an organic compound that serves as a host(hereinafter referred to as host material) are subjected toco-evaporation to form a 300 nm thick film as the light emitting layer705. An organic compound capable of blocking carriers, bathocuproin(hereinafter referred to as BCP), is formed into a 10 nm thick film asthe blocking layer 706. Then tris (8-quinolinolate) aluminum(hereinafter referred to as Alq₃), which is an organic compound capableof transporting electrons, is formed into a 40 nm thick film as theelectron transporting layer 707. The organic compound layer that emitsred light is thus obtained.

The organic compound layer that emits red light is formed from fivekinds of organic compounds having different functions in the casedescribed here. However, the present invention is not limited theretoand known materials can be used to form the organic compound layer thatemits red light.

An organic compound layer that emits green light is formed next.Specifically, α-NPD, which is an organic compound capable oftransporting holes, is formed into a 40 nm thick film as the holetransporting layer 704 on the first electrode (anode) 701 previouslyformed. Then CBP as a host material capable of transporting holes andtris (2-phenylpyridine) iridium (hereinafter referred to as Ir(ppy)₃),which is a luminous organic compound, are subjected to co-evaporation toform a 300 nm thick film as the light emitting layer 705. An organiccompound capable of blocking carriers, BCP, is formed into a 10 nm thickfilm as the blocking layer 706. Then Alq₃, which is an organic compoundcapable of transporting electrons, is formed into a 40 nm thick film asthe electron transporting layer 707. The organic compound layer thatemits green light is thus obtained.

The organic compound layer that emits green light is formed from fourkinds of organic compounds having different functions in the casedescribed here. However, the present invention is not limited theretoand known materials can be used to form the organic compound layer thatemits green light.

An organic compound layer that emits blue light is formed next.Specifically, α-NPD, which is a luminous organic compound capable oftransporting holes, is formed into a 40 nm thick film as the lightemitting layer 705 on the first electrode (anode) 701 previously formed.An organic compound capable of blocking carriers, BCP, is formed into a10 nm thick film as the blocking layer 706. Then Alq₃, which is anorganic compound capable of transporting electrons, is formed into a 40nm thick film as the electron transporting layer 707. The organiccompound layer that emits blue light is thus obtained.

The organic compound layer that emits blue light is formed from threekinds of organic compounds having different functions in the casedescribed here. However, the present invention is not limited theretoand known materials can be used to form the organic compound layer thatemits blue light.

By forming the organic compound films shown in the above on firstelectrode (anode), the pixel portion can have organic compound layersthat emit red light, organic compound layers that emit green light, andorganic compound layers that emit blue light.

Next, the second electrode (cathode) 673 is formed to cover the organiccompound layer 672 and the second insulating layer 671 as shown in FIG.6C. In this embodiment, the second electrode 673 is desirably formedfrom a material having a small work function in order to improveinjection of electrons. The second electrode (cathode) 673 is a laminateof a cathode buffer layer (not shown in the drawing) that is in contactwith the organic compound layer 672 and a conductive film. The cathodebuffer layer is formed of calcium fluoride (CaF₂) or barium fluoride(BaF₂). The conductive film is formed of aluminum. In this embodiment,the second electrode (cathode) 673 is obtained by forming a calciumfluoride film as the cathode buffer layer to a thickness of 1 nm andlaying thereon an aluminum film with a thickness of 100 nm.

Other known cathode materials can be used for the second electrode 673as long as it is a conductive film having a small work function.

In this way, a driving circuit 1705 having an n-channel TFT 1701 and ap-channel TFT 1702 can be formed on the same substrate where a pixelportion 1706 having a switching TFT 1703 that is an n-channel TFT and acurrent controlling TFT 1704 that is a p-channel TFT is formed (FIG.6C).

The pixel portion of the light emitting device which is shown in FIG. 1corresponds to the pixel portion 1706 shown in FIG. 6C. Here, the pixelportion 1706 and the driving circuit 1705 are formed at the same time.

In the pixel portion 1706, the switching TFT 1703 (n-channel TFT) has achannel formation region 503, the first impurity region (n⁻ region) 638,and the second impurity regions (n⁺ regions) 635. The first impurityregion 638 is formed outside of the conductive layer 623 for forming agate electrode. One of the second impurity regions 635 serves as asource region and the other serves as a drain region.

The current controlling TFT 1704 (p-channel TFT) of the pixel portion1706 has a channel formation region 504, the fourth impurity region (n⁻region) 644, and the fifth impurity regions (n⁺ regions) 642. The fourthimpurity region 644 is formed outside of the conductive layer 624 forforming a gate electrode. One of the fifth impurity regions 642 servesas a source region and the other serves as a drain region. In thepresent invention, one of the fifth impurity regions (n⁺ regions) 642 iselectrically connected to the electrode of the light emitting elementthrough the wire 657. The electrode is desirably the anode of the lightemitting element since the current controlling TFT 1704 is a p-channelTFT in this embodiment.

In the driving circuit 1705, the n-channel TFT 1701 has a channelformation region 501, the third impurity region (n⁻ region) 637, and thesecond impurity regions (n⁺ regions) 634. The third impurity region 637partially overlaps the conductive layer 621 for forming a gate electrodewith an insulating film sandwiched between the impurity region and theconductive layer. One of the second impurity regions 634 serves as asource region and the other serves as a drain region.

The p-channel TFT 1702 of the driving circuit 1705 has a channelformation region 502, the fifth impurity region (p⁻ region) 643, and thefourth impurity regions (p⁺ region) 641. The fifth impurity region 643partially overlaps the conductive layer 622 for forming a gate electrodewith an insulating film sandwiched between the impurity region and theconductive layer. One of the fourth impurity regions 641 serves as asource region and the other serves as a drain region.

By combining the TFTs 1701 and 1702 suitably, a shift register circuit,a buffer circuit, a level shifter circuit, a latch circuit, and the likeare formed to build the driving circuit 1705. If a CMOS circuit is to beformed, for example, the n-channel TFT 1701 and the p-channel TFT 1702are connected complementarily.

For a circuit that gives highest importance to reliability, then-channel TFT 1701 is suitable because it has a GOLD (Gate-drainOverlapped LDD) structure in which an LDD (Lightly Doped Drain) regionoverlaps a gate electrode with a gate insulating film interposedtherebetween.

The TFTs in the driving circuit 1705 (the n-channel TFT and thep-channel TFT) are required to have high drive performance (ON current:Ion) and to prevent degradation due to the hot carrier effect forimproved reliability. Accordingly, this embodiment uses TFTs each havinga region (GOLD region) where a gate electrode overlaps a lowconcentration impurity region with a gate insulating film interposedtherebetween as a structure effective in preventing hot carriers fromlowering the ON current value.

In contrast, the switching TFT 1703 of the pixel portion 1706 isrequired to have low OFF current (Ioff). Accordingly, this embodimentuses a TFT having a region (LDD region) where a gate electrode does notoverlap a low concentration impurity region with a gate insulating filminterposed therebetween as a TFT structure for lowering OFF current.

In the process of manufacturing a light emitting device of thisembodiment, the material of a gate electrode is used to form a sourcesignal line and the wire material for forming source and drainelectrodes is used to form a gate signal line because of circuitstructures and how the manufacture proceeds. However, the electrodes andsignal lines can be formed from different materials.

FIG. 8A shows a detailed top structure of the pixel portion of the lightemitting device described in this embodiment. A circuit diagram thereofis shown in FIG. 8B. FIGS. 8A and 8B use common symbols and can becross-referred.

In FIG. 8A, a switching TFT 800 provided on a substrate is the switching(n-channel) TFT 1703 of FIGS. 6A to 6C. For the structure of theswitching TFT 800, see the description of the switching (n-channel) TFT1703. A wire denoted by 802 is a gate wire for electrically connectinggate electrodes 801 (801 a and 801 b) of the switching TFT 800.

In this embodiment, the TFT has a double gate structure in which twochannel formation regions are formed. However, it may take a single gatestructure having one channel formation region or a triple gate structurehaving three channel formation regions.

The source of the switching TFT 800 is connected to a source wire 803,and the drain thereof is connected to a drain wire 804. The drain wire804 is electrically connected to a gate electrode 806 of a currentcontrolling TFT 805. The current controlling TFT 805 is the currentcontrolling (p-channel) TFT 1704 of FIGS. 6A to 6C. For the structure ofthe current controlling TFT 805, see the description of the currentcontrolling (p-channel) TFT 1704. The current controlling TFT 805 inthis embodiment has a single gate structure, but it may take a doublegate structure or a triple gate structure.

The source of the current controlling TFT 805 is electrically connectedto a current supply line 807, and the drain thereof is electricallyconnected to a drain wire 808. The drain wire 808 is electricallyconnected to a first electrode (anode) 809 indicated by the dotted line.

A wire denoted by 810 is a gate wire electrically connected to a gateelectrode 812 of an erasing TFT 811. The source of the erasing TFT 811is electrically connected to the current supply line 807, and the drainthereof is electrically connected to the drain wire 804.

Manufacture of the erasing TFT 811 is similar to the manufacture of thecurrent controlling (p-channel) TFT 1704 of FIGS. 6A to 6C. For thestructure of the erasing TFT 811, see the description of the currentcontrolling (p-channel) TFT 1704. The erasing TFT 811 in this embodimenthas a single gate structure, but it may take a double gate structure ora triple gate structure.

Capacitor storage (capacitor) is formed in a region denoted by 813. Thecapacitor 813 is formed among a semiconductor film 814 that iselectrically connected to the current supply line 807, an insulatingfilm (not shown in the drawing) on the same layer as the gate insulatingfilm, and the gate electrode 806. A capacitance formed by the gateelectrode 806, the same layer (not shown in the drawing) as the firstinterlayer insulating film and the second interlayer insulating film,and the current supply line 807 can also be used as capacitor storage.

A light emitting element 815 shown in the circuit diagram of FIG. 8B iscomposed of a first electrode (anode) 809, an organic compound layer(not shown in the drawing) formed on the first electrode (anode) 809,and a second electrode (cathode) (not shown in the drawing) formed onthe organic compound layer. In the present invention, the firstelectrode (anode) 809 is connected to the source region or drain regionof the current controlling TFT 805.

An opposite electric potential is given to the second electrode(cathode) of the light emitting element 815. A power supply electricpotential is given to a current supply line V. The difference betweenthe opposite electric potential and the power supply electric potentialis always kept at a level large enough to cause the light emittingelement to emit light when the anode receives the power supply electricpotential. The power supply electric potential and the opposite electricpotential are given by power supplies provided by an IC or the likeexternal to the light emitting device of the present invention. Thepower supply for providing the opposite electric potential isparticularly called an opposite power source 816 in this specification.

In this embodiment, the drive voltage of the TFTs is 1.2 to 10 V,preferably 2.5 to 5.5 v.

When an animation is displayed, the background image is formed by pixelswhose light emitting elements are emitting light whereas texts aredisplayed by pixels whose light emitting elements are not emittinglight. When an animation displayed is still for more than a given period(called stand-by in this specification), the display method is switched(inverted) to save power. Specifically, texts are displayed by pixelswhose light emitting elements are emitting light (also called textdisplay) whereas the background image is formed by pixels whose lightemitting elements are not emitting light (also called backgrounddisplay).

Embodiment 3

This embodiment describes with reference to FIGS. 9A and 9B the exteriorof an active matrix light emitting device of the present invention. FIG.9A is a top view of the light emitting device, and FIG. 9B is asectional view taken along the line A-A′ in FIG. 9A. Regions 901, 902,and 903 indicated by dotted lines are a source signal line drivingcircuit, a pixel portion, and a gate signal line driving circuit,respectively. Denoted by 904 is a sealing substrate and 905 denotes aseal agent. The seal agent 905 surrounds a space 907.

Denoted by 908 is a wire for sending signals to be inputted to thesource signal line driving circuit 901 and the gate signal line drivingcircuit 903. The wire 908 receives a video signal and a clock signalfrom an FPC (flexible printed circuit) 909 that serves as an externalinput terminal. Although the FPC alone is shown here, a printed wireboard (PWB) may be attached to the FPC. In this specification, a lightemitting device includes a light emitting device itself plus an FPCand/or PWB attached thereto.

Referring to FIG. 9B, the sectional structure is described next. Drivingcircuits and a pixel portion are formed on a substrate 910. However,FIG. 9B only show the source signal line driving circuit 901 as adriving circuit and the pixel portion 902.

The source signal line driving circuit 901 is a CMOS circuit that is acombination of an n-channel TFT 913 and a p-channel TFT 914. TFTsconstituting the driving circuits may form a known CMOS circuit, PMOScircuit, or NMOS circuit. The light emitting device shown in thisembodiment is a driver-integrated type in which driving circuits areformed on a substrate. However, driving circuits arc not necessarilyformed on a substrate and they may be external to the substrate.

The pixel portion 902 is composed of a plurality of pixels. Each pixelincludes a current controlling TFT 911 and a first electrode (anode) 912that is electrically connected to the drain of the current controllingTFT 911.

Insulating layers 913 is formed at both ends of the first electrode(anode) 912. An organic compound layer 914 is formed on the firstelectrode (anode) 912. A second electrode (cathode) 916 is formed on theorganic compound layer 914. In this way, a light emitting element 918composed of the first electrode (anode) 912, the organic compound layer914, and the second electrode (cathode) 916 is formed.

The second electrode (cathode) 916 also functions as a wire common toall pixels, and is electrically connected to an FPC 909 through aconnection wire 908.

The sealing substrate 904 is bonded by the seal agent 905 in order toseal the light emitting element 918 formed on the substrate 910. Aspacer formed from a resin film may be provided to keep the gap betweenthe sealing substrate 904 and the light emitting element 918. The space907 inside the seal agent 905 is filled with inert gas such as nitride.The seal agent 905 is preferably an epoxy-based resin. It is alsodesirable to use as the seal agent 905 a material that allows as littlemoisture and oxygen as possible to transmit. A substance having aneffect of absorbing oxygen and water may be put in the space 907.

The sealing substrate 904 in this embodiment can be a glass substrate ora quartz substrate. In addition, a plastic substrate formed of FRP(Fiberglass-Reinforced Plastics), PVF (polyvinyl fluoride), Mylar,polyester, acrylic, etc. can be used as the sealing substrate. After thesealing substrate 904 is bonded using the seal agent 905, more sealagent may be used so as to cover the side faces (exposed faces) forsealing.

By sealing the light emitting element in the space 907 as describedabove, the light emitting element is completely cut off from the outsideand external substances that accelerate degradation of the organiccompound layer, such as moisture and oxygen, can be prevented fromentering the element. Accordingly, a highly reliable light emittingdevice can be obtained.

The structure of this embodiment can be combined freely with anystructures shown in Embodiments 1 and 2.

Embodiment 4

Light emitting devices using light emitting elements are self-luminousand therefore have better visibility in bright surroundings and widerview than liquid crystal display devices. Accordingly, a light emittingdevice of the present invention can be used to obtain various electricappliances.

Examples of electronic appliance manufactured using the light emittingdevices formed with the present invention include, video cameras,digital cameras, goggle type displays (head mounted displays),navigation systems, audio reproducing devices (car audios, and audiocomponents, etc.), notebook computers, game machines, portableinformation terminals (mobile computers, mobile telephones, mobile typegame machines, and electronic book devices, etc.), image reproducingdevices equipped with a recording medium (specifically digital videodisks (DVDs), etc. that reproduces the recording medium and devicesequipped with a display device that displays the image) and the like. Inparticular, as to the portable information terminals, there is a lot ofan opportunity to look at the screen from a diagonal direction. Then, asthe extent of angle of visibility is regarded as important, a lightemitting device with a light emitting element is desirably used.Examples of these electronic appliances are specifically shown in FIG.10.

FIG. 10A is a display device, which is composed of a frame 2001, asupport base 2002, a display unit 2003, a speaker portion 2004, a videoinput terminal 2005, and the like. The light emitting devicemanufactured by the present invention is used for the display unit 2003to be manufactured. Light emitting devices with light emitting elementsare self-luminous and therefore do not need a backlight, thereby makingit possible to obtain a thinner display unit than that of a liquidcrystal display device. The term display device includes all the displaydevices for displaying information, such as personal computer monitors,display devices for receiving TV broadcasting, and display devices foradvertising.

FIG. 10B is a digital still camera, which is composed of a main body2101, a display unit 2102, an image-receiving portion 2103, operationkeys 2104, an external connection port 2105, a shutter 2106, and thelike. The light emitting device manufactured by the present invention isused for the display unit 2102 to be manufactured.

FIG. 10C is a notebook type personal computer, which is composed of amain body 2201, a frame 2202, a display unit 2203, a keyboard 2204, anexternal connection port 2205, a pointing mouse 2206, and the like. Thelight emitting device manufactured by the present invention is used forthe display unit 2203 to be manufactured.

FIG. 10D is a mobile computer, which is composed of a main body 2301, adisplay unit 2302, a switch 2303, operation keys 2304, an infrared port2305, and the like. The light emitting device manufactured by thepresent invention is used for the display unit 2302 to be manufactured.

FIG. 10E is a portable image reproducing device provided with arecording medium (specifically, a DVD reproducing device), which iscomposed of a main body 2401, a frame 2402, a display unit A 2403, adisplay unit B 2404, a recording medium (such as a DVD) read-in portion2405, operation keys 2406, a speaker portion 2407, and the like. Thedisplay unit A 2403 mainly displays image information, and the displayunit B 2404 mainly displays character information, and the lightemitting device manufactured by the present invention is used for thedisplay unit A 2403 and display unit B 2404 to be manufactured. Notethat family game machines and the like are included in the category ofimage reproducing devices provided with a recording medium.

FIG. 10F is a goggle type display (head mounted display), which iscomposed of a main body 2501, a display unit 2502, an arm portion 2503,and the like. The light emitting device manufactured by the presentinvention is used for the display unit 2502 to be manufactured.

FIG. 10G is a video camera, which is composed of a main body 2601, adisplay unit 2602, a frame 2603, an external connection port 2604, aremote control receiving portion 2605, an image receiving portion 2606,a battery 2607, an audio input portion 2608, operation keys 2609, aneyepiece portion 2610, and the like. The light emitting devicemanufactured by the present invention is used for the display unit 2602to be manufactured.

FIG. 10H is a mobile telephone, which is composed of a main body 2701, aframe 2702, a display unit 2703, an audio input portion 2704, an audiooutput portion 2705, operation keys 2706, an external connection port2707, an antenna 2708, and the like. The light emitting devicemanufactured by the present invention is produced for the display unit2703 to be manufactured. Note that white characters are displayed on ablack background, whereby the display unit 2703 can suppress the powerconsumption of the mobile telephone.

Note that if the light emitting luminance of the organic materialincreases in the future, the expanding projection of the light includedin the outputted image information is performed with a lens or the like,whereby it is possible to use the projected light in front typeprojectors or read type projectors.

Electric appliances as those described above now increasingly displayinformation distributed through electronic communication lines such asInternet and CATV (cable television), particularly animationinformation. Since organic materials have very fast response, lightemitting devices are preferably in displaying animation.

In a light emitting device, areas that are emitting light consume powerand therefore information is preferably displayed in a manner that makesas small areas as possible to emit light. It is therefore preferable touse portions that are not emitting light for the background and portionsthat are emitting light for text information when a light emittingdevice is used as a display unit of a portable information terminal,particularly, cellular phone and an audio reproducing device wheremainly text information is displayed.

As described, the application range of a light emitting devicemanufactured in accordance with a manufacturing method of the presentinvention is so wide that the light emitting device of the presentinvention can be used in electric appliances of any field. The electricappliances of this embodiment can be obtained by using light emittingdevices that are manufactured in accordance with Embodiments 1 through3.

In the present invention, a film formed of an organic material and afilm formed of an inorganic material are layered to form an interlayerinsulating film. The obtained interlayer insulating film has both acharacteristic of an inorganic material which does not allow oxygen andmoisture to transmit and a characteristic of an organic material whichmakes it possible to form a thick film and level the surface well. Thisway a light emitting element can be protected against oxygen andmoisture and therefore degradation of the light emitting element can beprevented.

In a light emitting device of the present invention, a contact hole isformed where a film formed of an organic material has been removed.Therefore, the problem accompanying forming a contact hole where a filmformed of an organic material is present can be solved.

1. A light emitting device comprising: a switching element; a firstinsulating film comprising an inorganic material formed over theswitching element; a second insulating film comprising an organicmaterial formed over the first insulating film; a contact hole formed inthe first insulating film and the second insulating film; a thirdinsulating film comprising an inorganic material formed so as to cover afirst portion of the second insulating film; a light emitting elementformed over the third insulating film, said light emitting elementcomprising a first electrode, a light emitting layer, and a secondelectrode; a wire formed in the contact hole; and an insulating layerformed over the wire covering an edge of the first electrode, whereinthe insulating layer is in contact with a second portion of the secondinsulating film which is not covered by the third insulating film, andwherein the wire extends over a part of the second insulating film and apart of the third insulating film and the switching element iselectrically connected to the first electrode through the wire.
 2. Thelight emitting device according to claim 1 wherein said switchingelement is formed over a substrate.
 3. The light emitting deviceaccording to claim 1 wherein said light emitting layer comprises anorganic compound.
 4. A light emitting device comprising: a transistor; afirst insulating film comprising an inorganic material formed over thetransistor; a second insulating film comprising an organic materialformed over the first insulating film; a contact hole formed in a gateinsulating film of the transistor, the first insulating film and thesecond insulating film; a third insulating film comprising an inorganicmaterial formed so as to cover a first portion of the second insulatingfilm; a light emitting element comprising a first electrode, a lightemitting layer, and a second electrode formed over the third insulatingfilm; a wire formed in the contact hole, said wire in contact with agate insulating film of the transistor, the first insulating film andthe second insulating film in the contact hole; and an insulating layerformed over the wire and covering an edge of the first electrode,wherein the insulating layer is in contact with a second portion of thesecond insulating film which is not covered by the third insulatingfilm, and the third insulating film, and wherein the wire extends over apart of the second insulating film and a part of the third insulatingfilm and the transistor is electrically connected to the first electrodethrough the wire.
 5. The light emitting device according to claim 4wherein said transistor is a thin film transistor.
 6. The light emittingdevice according to claim 4 wherein said light emitting layer comprisesan organic compound.
 7. The light emitting device according to claim 1,wherein the inorganic material is a silicon oxynitride film or siliconnitride film, and wherein the silicon content ratio of the film is 25.0atomic % or higher and 35.0 atomic % or lower and the nitrogen contentratio thereof is 35.0 atomic % or higher and 65.0 atomic % or lower. 8.The light emitting device according to claim 4, wherein the inorganicmaterial is a silicon oxynitride film or silicon nitride film, andwherein the silicon content ratio of the film is 25.0 atomic % or higherand 35.0 atomic % or lower and the nitrogen content ratio thereof is35.0 atomic % or higher and 65.0 atomic % or lower.
 9. The lightemitting device according to claim 1, wherein the organic material isselected from the group consisting of acrylic, polyimide, polyamide,polyimideamide, and benzocyclobutene.
 10. The light emitting deviceaccording to claim 4, wherein the organic material is selected from thegroup consisting of acrylic, polyimide, polyamide, polyimideamide, andbenzocyclobutene.
 11. The light emitting device according to claim 1,wherein the light emitting device is one selected from the groupconsisting of a display device, a digital still camera, a notebookcomputer, a mobile computer, a portable image reproducing device with arecording medium, a goggle type display, a video camera, and a cellularphone.
 12. The light emitting device according to claim 4, wherein thelight emitting device is one selected from the group consisting of adisplay device, a digital still camera, a notebook computer, a mobilecomputer, a portable image reproducing device with a recording medium, agoggle type display, a video camera, and a cellular phone.
 13. A devicecomprising: a switching element; a first insulating film comprising aninorganic material formed over the switching element; a secondinsulating film comprising an organic material formed over the firstinsulating film; a contact hole formed in the first insulating film andthe second insulating film; a third insulating film comprising aninorganic material formed so as to cover a first portion of the secondinsulating film; a first electrode for a light emitting element; a wireformed in the contact hole; and an insulating layer formed over the wireand covering an edge of the first electrode, wherein the insulatinglayer is in contact with a second portion of the second insulating filmwhich is not covered by the third insulating film, and wherein the wireextends over a part of the second insulating film and a part of thethird insulating film and the switching element is electricallyconnected to the first electrode through the wire.
 14. The deviceaccording to claim 13 wherein said switching element is formed over asubstrate.
 15. The device according to claim 13, wherein the inorganicmaterial is a silicon oxynitride film or silicon nitride film, andwherein the silicon content ratio of the film is 25.0 atomic % or higherand 35.0 atomic % or lower and the nitrogen content ratio thereof is35.0 atomic % or higher and 65.0 atomic % or lower.
 16. The deviceaccording to claim 13, wherein the organic material is selected from thegroup consisting of acrylic, polyimide, polyamide, polyimideamide, andbenzocyclobutene.